ISPC 3.0.3.1 - how can I change nginx webserver port?

Question: I want to put Varnish in front of nginx, which must then listen on a different port, let's say 8084.

I've looked in the manual, I've looked through the control panel, I've tried changing the ports for that IP address, but I just don't see it.

Of course, I can manually change the port in the site.conf file, but then every single time I make another change, it puts it back again. So I have to ssh in, sudo, nano the file, save, restart nginx.... until the next time!